6 Symptoms of A Bad Idle Air Control (IAC) Valve (& Driving With It)

A vehicle is composed of so many parts that it gets overwhelming to talk about it. The idle air control valve is one of the not-so-known parts of a vehicle that does not get discussed often.

Usually, the spotlight is on a high-level understanding of an engine rather than the individual parts that make it. We’ll dig into the symptoms of a bad idle air control valve (also referred to as an IAC valve).

When riding a car, it does not run at the same speed all the time. Depending on several external elements such as traffic or weather, it goes fast or slow. A car that is not moving is idle. It means it will not make any sense if the engine behaves in the same manner when the car is moving.

Manufacturers invented it to address this behavior. Maybe you are interested in other engine-related articles and own a Thermo King reefer. We have also read an article that details its alarm fault codes.

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What does it do?

The idle air control valve is otherwise known as an idle air control actuator. It handles the rotational speed of an idle engine. What is even more interesting is that the idle speed is not the same all the time. Several factors such as load to the electrical system and temperature contribute to how slow or fast the idle speed is.

What are the 6 symptoms of a bad idle air control valve to look out for?

Just like any other mechanical component, it has the possibility of breaking down on occasion. If it goes bad after several years of service, it is not an indicator of poor quality. Still, rather it is common to happen in mechanical components.

What makes matters worse is that even when your vehicle acts up, you might not immediately suspect something wrong with this little-known part. You need to take a series of steps to determine which specific component is at fault. Below are six idle air control valve symptoms that usually show when it goes bad.

1. Did the check engine light come on?

The check engine light indicates that your vehicle has one or more issues. However, having it come on does not necessarily mean an issue. It comes on even if the vehicle does not have any problems, but that is rarely the case.

To be on the safer side of things, check for any possible issues with the vehicle when you see the light on. The problem could either be the valve or something else.

So, you might be wondering what causes the check engine light to switch on. Whenever the control unit picks up an irregular pattern with how the engine behaves while idle, the check light gets switched on.

Check the vehicle for possible issues. If you are still unsure if the issue is the valve that has gone bad, read on. See if there are any signs of the other possible symptoms below. Suppose the check engine light is on and combined with the other symptoms listed below. You are likely experiencing a problem with the valve.

2. Does the idle speed randomly fluctuate?

The idle speed of a vehicle is usually consistent. The idle speed is very much dependent on several external factors such as engine temperature and load. Given a particular condition, it should have consistent idle speed while it is in that condition.

Your engine is idling, and your RPM runs at 800 revolutions per minute. If it stays consistently at 800 RPM, you likely do not have any issues with your valve.

The problem begins if you notice your idle speed jumping all over the place. For example, your engine is idling and is running at 1000 RPM. A few minutes later, it goes down to 800 RPM and then to 900 RPM.

When your engine is left idling, and the inconsistency in RPM does not go away, it is a clear sign that there is an issue. Reach out to a professional as soon as possible. Do not take it for granted, as it may lead to more complicated issues when left unattended.

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3. Does the engine sound rougher on idle?

Vehicles manufactured years ago will have an outdated engine control unit that cannot compensate for problems the component has. As the technology behind the control unit got better, it reached a point at which it could make up for shortcomings with this crucial component.

4. Are you experiencing a vibrating feeling in the car?

When your vehicle’s engine sounds off on idle, the valve may be faulty. In most cases, a bad one will also produce a vibrating effect throughout the vehicle. If this is the case, you may need to have a professional check it as soon as possible.

So how do you know if it is working as expected and like it’s supposed to? You can determine this with the sound your engine is producing. An idle engine with minimal and unvarying sound is a sign that it is running smoothly.

5. Does the engine stall frequently?

It happens when it stops abruptly and suddenly stops operating. Experiencing a stall does not necessarily mean your engine is completely dead and won’t restart. It could die, then come back up after a few restart attempts.

One of the causes of a stall is a faulty valve. The engine will stall when it does not get enough air supply while it is idle. Another possible reason for the engine to stall is when the control unit cannot compensate for the valve’s issues.

Like any other mechanical issue, the engine stall will occasionally occur during the first few times. If you do not call for a professional to check the problem, it will occur more frequently.

6. Do you experience vehicle backfires?

If you see flames coming out from the vehicle’s exhaust pipe, that is known as a vehicle backfire. It backfires when combustion happens outside the combustion cylinders.

When it backfires, it could be another possible symptom. However, it is also consequential to know that it could indicate a completely different kind of issue. 

Accelerate your vehicle to determine if the backfires you are experiencing are due to this component has gone bad. Let it decelerate and observe if the vehicle twitches. 

Once you have done that, check the exhaust pipe for leaking. It is usually found at the vehicle’s rear. Suppose the vehicle twitches as it decelerates and fuel leaks from the exhaust pipe. It is most likely a problem related to the idle air control valve. Speaking of fuel, you may want to read about fuel transfer tanks.

What happens when it goes bad?

The idle air control valve is responsible for controlling the RPM when idle. It essentially puts the engine in a relaxed state whenever the power is not needed.

When it goes bad, the engine will stall. It means it may abruptly stop working. The effects usually gradually worsen in time. It may start with one to two stalls in a week and may worsen to three or more per day.

Here’s a real-world example. You are at a stoplight, and there are still 60 seconds left at the stop sign. If you lift your foot from the pedal, your engine will go on idle. If you have a bad IAC valve, it may abruptly stop working instead of going on idle.

To avoid any complications, consult a professional mechanic as soon as you experience at least one of the six symptoms. Find out what the symptoms are of a bad IAC valve. Doing so should save you from the possibility of spending more money.

Can you drive with a bad idle air control valve?

Yes, you can still drive with a bad idle air control valve. However, the more pressing question is should you drive a car with a bad one? Driving with a bad component is not advisable, especially not this one. A bad valve will cause your engine to stall, detrimental to your and your passenger’s safety.

It’s also important to know that a bad one could lead your vehicle to fail an emissions test.

How do I reset it?

There are a few reasons why you need to reset the valve. One common reason is the need to recalibrate it. Another reason to reset it is to make sure that the check engine light is not on by mistake.

Performing a reset is easy and takes a maximum of one minute. First, slightly press the accelerator pedal just before ignition. Then ignite your engine and leave it running for five seconds. Once that has passed, switch off the engine and wait for about ten seconds. Lastly, ignite your engine again and check if it is idling normally.

Suppose you have done the reset and are still facing issues with it. In that case, it is best to consult a mechanic for professional advice.

Is it stuck open?

If stuck open, it will operate as expected once it reaches an optimal RPM. When the engine starts from a cold state, it may shut down once a small puff of smoke goes out of the exhaust pipe. It is the result of an obstructed component. 

Hopefully, this article has given you a better idea of how to deal with an engine showing symptoms that need to be addressed. That pesky engine light may be an indication of system errors. It could also be that the IAC valve is starting to act up.

You may test it in various ways. You can even have it cleaned. It’s important to know that there comes a time when a replacement is probably inevitable.

Here is a list of the cars and manufacturers that seems to have a significant number of bad IAC valve cases. You should particularly be looking for the symptoms with any of these cars:

  • 1998 Dodge Ram
  • Dodge Dakota
  • 2000, 2001, 2002, 2003 Honda Accord
  • 2000 Honda Civic
  • Ford Explorer
  • 1999 Honda Accord
  • Jeep
  • 2003 Chevy Silverado
  • 94 Chevy 1500
  • 2000 Nissan Maxima
  • 4.3 Vortec

Whether you have a Miata P0505, it’s important to find its location and see what is going on.

Can a bad one cause hard starting?

Yes, a faulty valve can cause hard starting and rough idling. Make sure to check it out. As you can see above, most of the reported issues that we were able to find were with older vehicles. You shouldn’t let the fear of such a small component be something that worries you! Replacing it won’t be a major expense.

There will be times when you need to fix up a bad air control valve when the car isn’t idling at its best. That is when you need to do the following.



How do you fix an IAC valve?

  1. Unplug the electrical connector

    There will be a wire attached to the valve, which must be removed. This is the electrical connector that connects to the ECU. Unplug this and follow the next step.

  2. Unscrew the bolts

    You’ll find two bolts on either side of the valve. Unscrew them using a wrench or a spanner. Once you do this, the IAC valve will come free.

  3. Tape off the opening

    Now you’re going to need some good quality tape to close the opening left behind the valve. Do it to prevent any debris from getting inside the engine and causing trouble.

  4. Take a closer look at the valve.

    Now that you’ve got the valve in your hands, take a look at how dirty it is and what’s causing the trouble. You can expect to see some carbon deposits. In some cases, the valve gets stuck in a closed position which causes the car to idle poorly.

  5. Start the cleaning

    The most important step while cleaning is to keep the motor on top and the opening at the bottom. This is to prevent any liquid from sliding down into the motor. Find a throttle body cleaner or a carbon cleaner for this job.

  6. Spray into the valve

    Start the spraying inside the valve and onto the carbon deposits. You can place a bowl or a glass jar underneath to catch all the debris and liquid. When the deposit is black and not clear, you know the valve was in dire need of cleaning. That’s what was causing all the trouble while idling.

  7. Scrub

    Use a thin pipe cleaner to scrub away inside the valve, and this will remove any leftover dust and carbon. Give it another spray after doing this, and you’re all set.

  8. Reinstall the valve

    Reversing the process you used to unplug the valve, you can reinstall it and test your car’s idling position. See how effective the fixing and cleaning have been.

What happens if you unplug your idle air control valve?

The natural reaction of a working, idle air control valve is that it would disturb your inactive engine if you unplug it. Under normal conditions, your idle air control valve adjusts itself according to the car’s RPMs. If this isn’t the case, when you unplug your idle air control valve, you know it has malfunctioned.

What is the function of the IAC valve?

The IAC is located on the fuel-injected engines of cars. It works alongside the car’s electronic control unit (ECU) to allow smooth airflow in regulated amounts to the engine. This makes for a better experience when the car is idling or, in other words running with the engine on although not moving.

How much does it cost to replace an idle air control valve?

When it fails, you will have to replace it with a new one. It is up to you if you will replace it with one that is the same as the original one. You can also replace it with a third-party brand that is compatible with your engine.

The cost of this component depends on your vehicle’s manufacturer and model. It could cost as low as $70 or as high as $500. Expect it will be cheaper to replace it for vehicles belonging to the budget class than vehicles belonging to the luxury class. 

Aside from the cost of the part, you also must factor in the cost of labor for replacing it. The cost of labor will depend on the shop where you will have it replaced. The labor cost is free in some cases if you purchase the part from the same shop.

How long do idle air control valves last?

3-4 years. A vehicle whose valve is in excellent condition is a huge factor to consider when determining its condition. A bad one leads to inconsistent idle speeds, which may cause more serious issues in the long run.

It is responsible for keeping your vehicle running when you are at a stoplight. It is also responsible for normalizing the RPM on idle. 

It is such a vital part of a vehicle that it should last as long as its life. Given how much work it needs to do to keep the vehicle running smoothly, it will eventually reach its end of life. It is normal for mechanical parts.

If the component has reached its end of life does not necessarily mean the vehicle has reached its end of life. Sometimes, it wears out ahead. It means you will have to replace it with a new one if you do not have plans to get a new vehicle.